1. Field of the Invention
The present invention relates to a valve-operation control system for an internal combustion engine, wherein the operating characteristics of an intake valve and an exhaust valve can be changed in accordance with the operational state of the engine.
2. Description of the Prior Art
A valve-operation control system for an internal combustion engine is conventionally known from Japanese Patent Application Laid-open No. 264123/90, in which a technique for operating a particular cylinder in a 4-cycle mode and stopping other cylinders in a low loading of the engine and for operating all the cylinders in a 6-cycle in a high loading of the engine is achieved by a timing of opening and closing of electromagnetically driven intake and exhaust valves.
When the temperature of an exhaust gas flowing into a catalytic converter incorporated in an exhaust system is low, a large amount of harmful hydrocarbon is discharged due to the fact that the temperature of a catalyst within the catalytic converter does not reach an activating temperature. When the engine is at an extremely low speed such as at a low-temperature start, it is desired that the temperature of the exhaust gas be promptly increased, but in the prior art system a prompt increase in the temperature of the exhaust gas cannot be expected.